Electro-optic device with semiconductor junction area and related methods

ABSTRACT

An electro-optic device may include a photonic chip having an optical grating coupler at a surface. The optical grating coupler may include a first semiconductor layer having a first base and first fingers extending outwardly from the first base. The optical grating coupler may include a second semiconductor layer having a second base and second fingers extending outwardly from the second base and being interdigitated with the first fingers to define semiconductor junction areas, with the first and second fingers having a non-uniform width. The electro-optic device may include a circuit coupled to the optical grating coupler and configured to bias the semiconductor junction areas and change one or more optical characteristics of the optical grating coupler.

TECHNICAL FIELD

The present disclosure relates to the field of photonics, and, moreparticularly, to an electro-optic device and related methods.

BACKGROUND

Integrated optical devices for directly processing optical signals havebecome of greater importance as optical fiber communicationsincreasingly replace metallic cable and microwave transmission links.Integrated optical devices can advantageously be implemented as siliconoptical circuits having compact dimensions at relatively low cost.Silicon optical circuits employ integrated waveguide structures formedin a silicon layer of a silicon on insulator (S01) substrates, to form asilicon photonic chip.

In some applications, the optical signal is injected in/extracted fromthe photonic chip in a near perpendicular fashion, with respect to thephotonic chip substrate plane, by means of optical grating couplersformed in the silicon photonic chip for input-output of the photonicsignal. When using the silicon substrate in such a coupling fashion,such as when coupling to an optical fiber, the optical fiber is mountedin near perpendicular fashion.

SUMMARY

Generally speaking, an electro-optic device may include a photonic chiphaving an optical grating coupler at a surface thereof. The opticalgrating coupler may comprise a first semiconductor layer of a firstconductivity type and comprising a first base and a first plurality offingers extending outwardly therefrom. The optical grating coupler maycomprise a second semiconductor layer of a second conductivity typecomprising a second base and a second plurality of fingers extendingoutwardly therefrom and being interdigitated with the first plurality offingers to define a plurality of semiconductor junction areas. The firstand second pluralities of fingers may have a non-uniform width. Theelectro-optic device may include a circuit coupled to the opticalgrating coupler and configured to bias the plurality of semiconductorjunction areas and change at least one optical characteristic of theoptical grating coupler.

In some embodiments, the first plurality of fingers may extendvertically past the second plurality of fingers to define a plurality ofrecesses respectively aligned with the second plurality of fingers.Also, the first base may have first and second ends, and the firstfingers may progressively increase in width from the first end to thesecond end. The first and second pluralities of fingers may be curved.

Additionally, the photonic chip may comprise first and second terminalscoupled respectively to the first and second bases. For example, the atleast one optical characteristic comprises at least one of a peak powerwavelength, an optical loss, and a refractive index. The electro-opticdevice may further include an optical element defining an optical pathabove the optical grating coupler. For example, the optical element maycomprise an optical fiber.

Another aspect is directed to an electro-optic device comprising aphotonic chip having an optical grating coupler at a surface thereof.The optical grating coupler may include a first semiconductor layer of afirst conductivity type, and a second semiconductor layer of a secondconductivity type. The first semiconductor layer may include a firstbase, and a first plurality of ridges extending outwardly from the firstbase to define a semiconductor junction area The first plurality ofridges may have a non-uniform width. The electro-optic device mayinclude a circuit coupled to the optical grating coupler and configuredto bias the semiconductor junction area and change at least one opticalcharacteristic of the optical grating coupler.

More specifically, the first plurality of ridges may extend verticallyto define a plurality of recesses between adjacent ridges. The firstbase may have first and second ends, and the first ridges mayprogressively increase in width from the first end to the second end.The first plurality of ridges may be curved.

Another aspect is directed to a method of making an electro-opticdevice. The method may include forming a photonic chip having an opticalgrating coupler at a surface thereof. The optical grating coupler mayinclude a first semiconductor layer of a first conductivity type andcomprising a first base and a first plurality of fingers extendingoutwardly therefrom, and a second semiconductor layer of a secondconductivity type. The second semiconductor layer may comprise a secondbase and a second plurality of fingers extending outwardly therefrom andbeing interdigitated with the first plurality of fingers to define aplurality of semiconductor junction areas. The first and secondpluralities of fingers may have a non-uniform width. The method mayinclude coupling a circuit to the optical grating coupler and beingconfigured to bias the plurality of semiconductor junction areas andchange at least one optical characteristic of the optical gratingcoupler.

Another aspect is directed to a method for making an electro-opticdevice. The method may include forming a photonic chip having an opticalgrating coupler at a surface thereof. The optical grating coupler mayinclude a first semiconductor layer of a first conductivity type, and asecond semiconductor layer of a second conductivity type. The firstsemiconductor layer may comprise a first base, and a first plurality ofridges extending outwardly from the first base to define a semiconductorjunction area, the first plurality of ridges having a non-uniform width.The method may include coupling a circuit to the optical grating couplerand being configured to bias the semiconductor junction area and changeat least one optical characteristic of the optical grating coupler.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic cross-section view of an electro-optic devicealong line 1A-1A of FIG. 1B, according to the present disclosure.

FIG. 1B is a schematic top plan view of the electro-optic device of FIG.1A.

FIG. 2A is a schematic cross-section view of another embodiment of theelectro-optic device along line 2A-2A of FIG. 2B, according to thepresent disclosure.

FIG. 2B is a schematic top plan view of the electro-optic device of FIG.2A.

FIG. 3 is a schematic top plan view of an electro-optic system,according to the present disclosure.

FIG. 4 is a schematic top plan view of another embodiment of theelectro-optic system, according to the present disclosure.

FIG. 5 is a diagram illustrating performance in an example embodiment ofthe electro-optic device, according to the present disclosure.

DETAILED DESCRIPTION

The present disclosure will now be described more fully hereinafter withreference to the accompanying drawings, in which several embodiments ofthe invention are shown. This present disclosure may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the present disclosure to those skilled in theart. Like numbers refer to like elements throughout, and prime notationis used to indicate similar elements in alternative embodiments.

Referring initially to FIGS. 1A-1B, an electro-optic device 10 accordingto the present disclosure is now described. The electro-optic device 10illustratively includes a photonic chip 26 having an optical gratingcoupler 11 at a surface thereof. The photonic chip 26 illustrativelyincludes a substrate 20, an insulator layer 21 on the substrate, and alayer 27 over the substrate. The layer 27 may comprise a semiconductorstack of dielectric layers.

The optical grating coupler 11 illustratively includes a firstsemiconductor layer 14 of a first conductivity type (e.g. N-type) andcomprising a first base 18 and a first plurality of fingers 19 a-19 bextending outwardly from the first base. The optical grating coupler 11illustratively includes a second semiconductor layer 15 of a secondconductivity type (e.g. P-type) comprising a second base 16 and a secondplurality of fingers 17 a-17 b extending outwardly from the second base.The first and second semiconductor layers 14, 15 are formed on theinsulator layer 21 (i.e. in the illustrated embodiment, a buried oxide(BOX) arrangement).

The second plurality of fingers 17 a-17 b is interdigitated with thefirst plurality of fingers 19 a-19 b to define a plurality ofsemiconductor junction areas 25 a-25 b. The first and second pluralitiesof fingers 19 a-19 b, 17 a-17 b have one or more of a non-uniform width(i.e. non-uniform width along the length of each finger and/or eachfinger having different widths), a non-uniform pitch, and a non-uniformperiodicity. In other embodiments, the first and second pluralities offingers 19 a-19 b, 17 a-17 b may have uniform widths. The first andsecond pluralities of fingers 19 a-19 b, 17 a-17 b are curved in theillustrated embodiment. In other embodiments, the first and secondpluralities of fingers 19 a-19 b, 17 a-17 b may be parallel inrectangular/square shaped patterns, for example.

The electro-optic device 10 illustratively includes an optical element13 defining an optical path above the optical grating coupler 11. Forexample, the optical element 13 may comprise an optical fiber, such as a10 μm fiber core, adjacent to the optical grating coupler 11.

The electro-optic device 10 illustratively includes a circuit (e.g.integrated circuit) 12 coupled to the optical grating coupler 11 andconfigured to bias the plurality of semiconductor junction areas 25 a-25b and change at least one optical characteristic of the optical gratingcoupler 11. In some embodiments, the circuit 12 and the optical gratingcoupler 11 are integrated on the same semiconductor device/substrate. Inyet other embodiments, the circuit 12 and the optical grating coupler 11are on separate semiconductor devices. Additionally, the circuit 12 maycomprise electro-optic driving circuitry, as will be appreciated bythose skilled in the art.

Additionally, the photonic chip 26 illustratively includes first andsecond terminals (e.g. copper or aluminum) 22, 23 respectively coupledto the first and second bases 18, 16 of the first and secondsemiconductor layers 14, 15. Via electric biasing, the circuit 12controls the first and second terminals 22, 23 to change a plurality ofoptical characteristics of the optical grating coupler 11. The pluralityof optical characteristics may comprise, for example, at least one of apeak power wavelength, an optical loss, and a refractive index. Inparticular, using the first and second terminals 22, 23, the circuit 12can bias the plurality of semiconductor junction areas 25 a-25 b to addcurrent flow (direct mode) or a depletion region (lower loss, reversemode) in the optical grating coupler 11. Also, by biasing the pluralityof semiconductor junction areas 25 a-25 b, the optical grating coupler11 coupler response will shift (affecting peak wavelength and loss).

In the illustrated embodiment, the first plurality of fingers 19 a-19 bextend vertically past the second plurality of fingers 17 a-17 b todefine a plurality of recesses 24 a-24 b respectively aligned with thesecond plurality of fingers, thereby defining an optical gratingcoupler. Also, the first base 18 illustratively includes first andsecond ends, and the first fingers 19 a-19 b progressively increase inwidth from the first end to the second end.

Another aspect is directed to a method of making the electro-opticdevice 10. The method includes forming a photonic chip 26 having anoptical grating coupler 11 at a surface thereof. The optical gratingcoupler 11 includes a first semiconductor layer 14 of a firstconductivity type and comprising a first base 18 and a first pluralityof fingers 19 a-19 b extending outwardly therefrom. The optical gratingcoupler 11 includes a second semiconductor layer 15 of a secondconductivity type comprising a second base 16 and a second plurality offingers 17 a-17 b extending outwardly therefrom and being interdigitatedwith the first plurality of fingers 19 a-19 b to define a plurality ofsemiconductor junction areas 25 a-25 b, the first and second pluralitiesof fingers having a non-uniform width. The method includes coupling acircuit 12 to the optical grating coupler 11 and being configured tobias the plurality of semiconductor junction areas 25 a-25 b and changeat least one optical characteristic of the optical grating coupler 11.

Referring now additionally to FIGS. 2A-2B, another embodiment of theelectro-optic device 10′ is now described. In this embodiment of theelectro-optic device 10′, those elements already discussed above withrespect to FIGS. 1A-1B are given prime notation and most require nofurther discussion herein. This embodiment of the electro-optic device10′ illustratively includes a photonic chip 26′ having an opticalgrating coupler 11′ at a surface thereof. The optical grating coupler11′ illustratively includes a first semiconductor layer 14′ of a firstconductivity type, and a second semiconductor layer 15′ of a secondconductivity type opposite the first conductivity type. The firstsemiconductor layer 14′ illustratively includes a first base 18′, and afirst plurality of ridges 19 a′-19 b′ extending outwardly from the firstbase to define a semiconductor junction area 25′. The first plurality ofridges 19 a′-19 b′ has a non-uniform width. In other embodiments, thefirst plurality of ridges 19 a′-19 b′ may have a uniform width. Theelectro-optic device 10′ illustratively includes a circuit 12′ coupledto the optical grating coupler 11′ and configured to bias thesemiconductor junction area 25′ and change at least one opticalcharacteristic of the optical grating coupler 11′.

More specifically, the first plurality of ridges 19 a′-19 b′illustratively extend vertically to define a plurality of recesses 24a′-24 b′ between adjacent pairs of ridges. The first base 18′illustratively includes first and second ends, and the first ridges 19a′-19 b′ progressively increase in width from the first end to thesecond end. The first plurality of ridges 19 a′-19 b′ are illustrativelycurved.

Another aspect is directed to a method for making the electro-opticdevice 10′. The method includes forming a photonic chip 26′ having anoptical grating coupler 11′ at a surface thereof. The optical gratingcoupler 11′ includes a first semiconductor layer 14′ of a firstconductivity type, and a second semiconductor layer 15′ of a secondconductivity type opposite the first conductivity type. The firstsemiconductor layer 14′ illustratively includes a first base 18′, and afirst plurality of ridges 19 a′-19 b′ extending outwardly from the firstbase to define a semiconductor junction area 25′. The first plurality ofridges 19 a′-19 b′ illustratively have a non-uniform width. The methodincludes coupling a circuit 12′ to the optical grating coupler 11′ andbeing configured to bias the semiconductor junction area 25′ and changeat least one optical characteristic of the optical grating coupler 11′.

Referring now to FIG. 3, an electro-optic system 30″ illustrativelyincludes first and second optical grating couplers 11 a″, 11 b″, and anoptical waveguide 34″ coupled between the first and second opticalgrating couplers. In this example electro-optic system 30″, the firstoptical grating coupler 11 a″ is similar to the embodiment depicted inFIGS. 2A-2B, and the second optical grating coupler 11 b″ is similar toa typical optical grating coupler. In this example application, thefirst optical grating coupler 11 a″ is configured to receive a constantoptical source signal 31″, and modulate the constant optical sourcesignal via an electrical command signal 33″ applied to the first andsecond terminals of the first optical grating coupler 11 a″. Theelectrical command signal 33″ shifts the phase of the constant opticalsource signal 31″. The second optical grating coupler 11 a″ isconfigured to generate a modulated optical signal 32″.

Referring now to FIG. 4, an electro-optic system 30′″ illustrativelyincludes first and second optical grating couplers 11 a′″, 11 b′″, andan optical waveguide 34′″ coupled between the first and second opticalgrating couplers. In this example electro-optic system 30′′, the firstand second optical grating couplers 11 a′″, 11 b′″ are similar to theembodiment depicted in FIGS. 2A-2B. In this example application, thefirst optical grating coupler 11 a′″ is configured to receive a constantoptical source signal 31′″, and modulate the constant optical sourcesignal via an electrical command signal 33′″ applied to the first andsecond terminals of the first optical grating coupler 11 a′″. Theelectrical command signal 33′″ shifts the phase of the constant opticalsource signal 31′″. The second optical grating coupler 11 a′″ isconfigured to generate a modulated optical signal 32′″, and a modulatedelectrical signal 35′″ at the respective terminals.

Advantageously, the electro-optic device 10 is able to modify or adjustthe optical coupler response of the optical grating coupler 11. In someembodiments (FIGS. 3-4), a control loop can be use to provide an opticalpower modulation. Also, by adding a resistive current path through theoptical grating coupler 11, the operational temperature of the opticalgrating coupler can be increased, thereby affecting one or more opticalcharacteristics. This provides the electro-optic device 10 with greateroperational flexibility than typical prior art devices, and also,provides a device capable of adapting optical performance to ambientconditions that affect optical performance.

In FIG. 4, by applying a modulation on both optical grating couplers 11a″-11 b″ (input, and output), the user can create a 4-level modulation,known as Power Amplitude Modulation (PAM4). That includes generating asignal taking 4 different levels, using two electrical signals, whichhas the advantage of increasing the data rate without increasing theclock frequency.

Indeed, with reference now to FIG. 5, the diagram 40 illustratesinsertion loss at varying wavelengths. In particular, curves 44, 43, 42,41 respectively demonstrate insertion loss at temperatures of 25° C.,50° C., 100° C., and 150° C., respectively. In the illustrated example,there is a 2 nm peak-wavelength shift for a 25° C. temperature change(i.e. 0.08 nm/° C.).

Compensation of the Temperature Variability (Which Causes Variation ofPeak Wavelength)

The characteristic of the optical grating coupler 11 (peak loss, peakwavelength, bandwidth) depends at first order on the effective index ofthe light in silicon waveguides. A grating coupler is based on the Braggself-interference of an optical signal going through material withalternative effective index (see, e.g., Wikipedia article on Fiber BraggGrating). A change in the effective index will change the Bragginterference wavelength, and thus the peak loss of the grating coupler.Thus, variation of effective index has consequences in variation of thepeak wavelength of the grating coupler. The temperature has a knowninfluence on the effective index. At 1310° K, the peak wavelength of agrating coupler has variation of ˜0.1 nm for a 1° K (dlambda/dT ˜0.1nm/K), considering a variation of effective index of 7E-5°/K (dneff/K)in the silicon.

Thus, by applying a voltage to the optical grating coupler 11, Applicantis able to compensate the effect of temperature variation. By applyingdynamically a voltage varying in function of the temperature, Applicantis able to create a temperature controlled loop to maintain the peakwavelength of the optical grating coupler 11. The compensation of thetemperature can be done in addition to the modulation, and thetemperature compensation is a slowly fluctuating bias (order <1 MHz),whereas the modulation signal is varying at frequency >1 Ghz

Compensation of the Process Variability

The thickness of a layer in a semiconductor is not uniform. There arecenter-border effects due to the technology used for semiconductorfabrication (i.e. etching, deposition, etc.). As a result, thecharacteristics of the optical grating coupler 11 are not uniform in asingle wafer. Variation observed is up to lOnm variation in peakwavelength. Thus by applying a constant voltage to the optical gratingcoupler 11, Applicant is able to compensate (i.e. detune) the effect ofprocess variability. Process compensation can be apply in addition totemperature compensation and modulation.

Many modifications and other embodiments of the present disclosure willcome to the mind of one skilled in the art having the benefit of theteachings presented in the foregoing descriptions and the associateddrawings. Therefore, it is understood that the present disclosure is notto be limited to the specific embodiments disclosed, and thatmodifications and embodiments are intended to be included within thescope of the appended claims.

That which is claimed is:
 1. An electro-optic device comprising: aphotonic chip having an optical grating coupler at a surface thereof,the optical grating coupler comprising a first semiconductor layer of afirst conductivity type and comprising a first base and a firstplurality of fingers extending outwardly therefrom, and a secondsemiconductor layer of a second conductivity type comprising a secondbase and a second plurality of fingers extending outwardly therefrom andbeing interdigitated with said first plurality of fingers to define aplurality of semiconductor junction areas, said first and secondpluralities of fingers having a non-uniform width; and a circuit coupledto said optical grating coupler and configured to bias said plurality ofsemiconductor junction areas and change at least one opticalcharacteristic of the optical grating coupler.
 2. The electro-opticdevice of claim 1 wherein said first plurality of fingers extendsvertically past said second plurality of fingers to define a pluralityof recesses respectively aligned with said second plurality of fingers.3. The electro-optic device of claim 1 wherein said first base has firstand second ends; and wherein said first fingers progressively increasein width from the first end to the second end.
 4. The electro-opticdevice of claim 1 wherein said first and second pluralities of fingersare curved.
 5. The electro-optic device of claim 1 wherein said photonicchip comprises first and second terminals coupled respectively to saidfirst and second bases.
 6. The electro-optic device of claim 1 whereinthe at least one optical characteristic comprises at least one of a peakpower wavelength, an optical loss, and a refractive index.
 7. Theelectro-optic device of claim 1 further comprising an optical elementdefining an optical path above said optical grating coupler.
 8. Theelectro-optic device of claim 7 wherein said optical element comprisesan optical fiber.
 9. An electro-optic device comprising: a photonic chiphaving an optical grating coupler at a surface thereof, the opticalgrating coupler comprising a first semiconductor layer of a firstconductivity type, and a second semiconductor layer of a secondconductivity type, the first semiconductor layer comprising a firstbase, and a first plurality of ridges extending outwardly from saidfirst base to define a semiconductor junction area, said first pluralityof ridges having a non-uniform width; and a circuit coupled to saidoptical grating coupler and configured to bias said semiconductorjunction area and change at least one optical characteristic of theoptical grating coupler.
 10. The electro-optic device of claim 9 whereinsaid first plurality of ridges extends vertically to define a pluralityof recesses between adjacent ridges.
 11. The electro-optic device ofclaim 9 wherein said first base has first and second ends; and whereinsaid first ridges progressively increase in width from the first end tothe second end.
 12. The electro-optic device of claim 9 wherein saidfirst plurality of ridges is curved.
 13. The electro-optic device ofclaim 9 wherein said photonic chip comprises first and second terminalscoupled respectively to said first base and said second semiconductorlayer.
 14. The electro-optic device of claim 9 wherein the at least oneoptical characteristic comprises at least one of a peak powerwavelength, an optical loss, and a refractive index.
 15. Theelectro-optic device of claim 9 further comprising an optical elementdefining an optical path above said optical grating coupler.
 16. Theelectro-optic device of claim 15 wherein said optical element comprisesan optical fiber.
 17. A method of making an electro-optic devicecomprising: forming a photonic chip having an optical grating coupler ata surface thereof, the optical grating coupler comprising a firstsemiconductor layer of a first conductivity type and comprising a firstbase and a first plurality of fingers extending outwardly therefrom, anda second semiconductor layer of a second conductivity type comprising asecond base and a second plurality of fingers extending outwardlytherefrom and being interdigitated with the first plurality of fingersto define a plurality of semiconductor junction areas, the first andsecond pluralities of fingers having a non-uniform width; and coupling acircuit to the optical grating coupler and being configured to bias theplurality of semiconductor junction areas and change at least oneoptical characteristic of the optical grating coupler.
 18. The method ofclaim 17 wherein the first plurality of fingers extends vertically pastthe second plurality of fingers to define a plurality of recessesrespectively aligned with the second plurality of fingers.
 19. Themethod of claim 17 wherein the first base has first and second ends; andwherein the first fingers progressively increase in width from the firstend to the second end.
 20. The method of claim 17 wherein the first andsecond pluralities of fingers are curved.
 21. The method of claim 17wherein the photonic chip comprises first and second terminals coupledrespectively to the first and second bases.
 22. The method of claim 17wherein the at least one optical characteristic comprises at least oneof a peak power wavelength, an optical loss, and a refractive index. 23.The method of claim 17 further comprising coupling an optical element todefine an optical path above the optical grating coupler.
 24. The methodof claim 23 wherein the optical element comprises an optical fiber. 25.A method for making an electro-optic device comprising: forming aphotonic chip having an optical grating coupler at a surface thereof,the optical grating coupler comprising a first semiconductor layer of afirst conductivity type, and a second semiconductor layer of a secondconductivity type, the first semiconductor layer comprising a firstbase, and a first plurality of ridges extending outwardly from the firstbase to define a semiconductor junction area, the first plurality ofridges having a non-uniform width; and coupling a circuit to the opticalgrating coupler and being configured to bias the semiconductor junctionarea and change at least one optical characteristic of the opticalgrating coupler.
 26. The method of claim 25 wherein the first pluralityof ridges extends vertically to define a plurality of recesses betweenadjacent ridges.
 27. The method of claim 25 wherein the first base hasfirst and second ends; and wherein the first ridges progressivelyincrease in width from the first end to the second end.
 28. The methodof claim 25 wherein the first plurality of ridges is curved.
 29. Themethod of claim 25 wherein the photonic chip comprises first and secondterminals coupled respectively to the first base and the secondsemiconductor layer.
 30. The method of claim 29 wherein the at least oneoptical characteristic comprises at least one of a peak powerwavelength, an optical loss, and a refractive index.
 31. The method ofclaim 25 further comprising coupling an optical element to define anoptical path above the optical grating coupler.
 32. The method of claim31 wherein the optical element comprises an optical fiber.